Fixed plate variable capacity condenser



June 3, G F BRETT r AL FIXED PLATE VARIABLE CAPACITY CONDENSER Filed Nov. 18, 1939 win INVENT R GEORGE pA/lzsufiu inerr NYMAN L vm ATTORNEY Patented June 3, 1941 FIXED PLATE VARIABLE CONDENS CAPACITY EB George Fairburn Brett, Chelmaiord, and Nyman Levin, Finchley, London, England, auignon to Radio Corporation oi America, a corporation of Delaware Application November 18, 1939, Serial No. 905,090

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The present invention relates to variable condensers.

According to this invention a variable condenser comprises at least two spaced condenser electrodes, a means for generating and directing a concentrated beam of electrons between said electrodes, means for receiving said beam, means for varying intensity of said beam and connections connecting said electrodes as condenser electrodes in an external circuit, the whole arrangement being such that variation of said intensity produces a variation oi the capacity between said electrodes.

The electron beam may be, for example, of flat ribbon form or of pencil form, and the condenser electrodes may have any of a wide variety of forms, e. g. ordinary parallel flat plates may be employed.

The electron beam may be produced by any suitable form of electron gun, e. g. by a gun having a rectilinear cathode, a control electrode, and an accelerating anode situated outside the space between the condenser electrodes, a collector anode being also positioned outside said space and opposite said gun to receive said beam.

The intensity of the beam may be varied in any of a number of ways, e. g. by varying the potential of the control electrode, or by varying the heating of the cathode.

If desired, a plurality of sets of electrodes constituting a plurality of electrically variable capacity condensers may be accommodated in a single evacuated envelope and a common gun or individual guns may be employed for said condensers. The condensers may be connected, if desired, within the envelope in parallel or otherwise as may be desired.

The invention is illustrated in the accompanying diagrammatic drawing which shows one em bodiment thereof.

Referring to the drawing there is provided within an evacuated envelope E, an electron gun including a rectilinear cathode K (e. g. an indirectly heated cathode) a slotted control electrode G, a slotted accelerating electrode A, and a slotted screen-suppressor electrode S, the slots in the several electrodes being aligned with one another and with the cathode so as to pass a ribbon-like beam of electrons, represented in broken lines. Also within the envelope is a pair of condenser electrodes C1, C2, situated one on each side of the path of the electron beam produced by the gun. Beyond the electrodes C1, C2 and in the direction of projection of the beam, is a collector electrode R. The screen-suppressor Great Britain November 12. 1938 electrode S serves, inter alia, to screen the electrodes C1, C2, from influence by any high frequency potentials applied to the control electrode G and to prevent the return of electrons from the collector electrode R to the electrodes of the gun system.

A condenser as above described and illustrated may be used for a variety oi. purposes. For example as shown, it may be used in conjunction with a tuned circuit. In the case illustrated, the electronically variable condenser C1, C2, is connected at PQ across the lumped condenser C and inductance L of the tuned circuit. Control of the potential on the control electrode G and hence of the total capacity of the tuned circuit (which consists of the inductance L, the capacity C and the capacity C1C2 in parallel therewith) may be either manually or automatically effected. Automatic variation can be effected at high frequency owing to the practically inertialess nature of the electron beam so that capacity variation can also be effected at high frequency.

If desired an electronically variable condenser as above described may be used to compensate for variations due to warming up of valves in a radio transmitter or like system. In such a case the intensity oi beam current in the condenser may be controlled by varying the temperature of the cathode thereof, which would be matched to the warming up time of the valves, the increase 01 beam current in the condenser gradually producing a decrease of capacity between the two condenser electrodes such as to compensate for increases in capacity of the valves.

The invention is not limited to the particular discharge tube arrangement illustrated. For example, the electron gun may be constituted by a known assembly oi! slotted concentric cylinders instead of by the assembly of slotted flat plates illustrated.

At flrst sight, the tube illustrated appears diagrammatically like the well known deflection type of electron beam valve wherein control of an electron beam is obtained by means of a pair of deflector plates positioned inthe places of the electrodes C1, C2. In the tube illustrated, however, there is only one beam collecting electrode, as distinct from the usual plurality of beam receiving surfaces of the known deflector type of tube, while, in use, the electrodes C1, C2 are normally at the same D. C. potential.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, what we claim is:

1. A system for electronically varying the capacity of a condenser, comprising an electron discharge tube having within an evacuated envelope a cathode, a control grid and an accelerating electrode constituting an electron gun which produces a concentrated beam of electrons, a collector electrode positioned to receive the beam from said gun, a pair of plate electrodes .con-

stituting the condenser the capacity of which is to be electronically varied situated one on each side of said beam and disposed in the space between said gun and said collector electrode, a

screen electrode at cathode potential between the condenser plate electrodes and the electron gun, and means for varying only the beam in- .tensity without deflecting the beam whereby the capacity between the condenser plate is altered.

2. A system for electronically varying the caelectrodes pacity of a utilization circuit, comprising an electron discharge tube having within an evacuated envelope a cathode, a control grid and an accelerating electrode constituting an electron gun which produces a concentrated beam of electrons, a single collector electrode positioned to receive the beam from said gun, a pair of spaced electrodes serving as a condenser situated one on GEORGE FAIRBURN BRET'I. NYMAN LEVIN. 

